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Kidney and Ureteral Stones

Kidney and ureteral stones may form when certain components in the urine become so concentrated that they form a solid crystal (a stone) within the kidney or urinary tract. Urine normally contains chemicals that prevent stones from forming, but when the amount of certain components are high and/or urine volume is low (less than 1 liter a day) the risk of developing stones increases. When stones do develop, urine may carry small stones out of the body causing little to no discomfort.

Many stones are as small as a grain of sand. They easily pass down the ureter into the bladder and out of the body through the urethra. Other stones may be pea- or marble-sized and more difficult to pass. Some stones are too large to pass out of the kidney—these are often called staghorn stones if they fill the renal pelvis—and some smaller stones may get trapped in the ureter, causing extreme pain, blockage of urine and bleeding into the urine.

The cause of kidney and ureteral stones depends on the type of stone you have.

Calcium stones are the most common, especially in men age 20-30. About 75 percent of kidney stones are made from calcium, in combination with either oxalate or phosphate. Oxalates occur naturally in some fruits and vegetables, as well as chocolate and nuts.

Uric acid stones occur when the urine is too acidic.

Struvite or infection stones form in some men and women who have a urinary tract infection. These stones can grow large and block the kidney, ureter or bladder.

Cysteine stones form in people who have cystinuria, a hereditary condition that causes the kidneys to excrete too much amino acid (cysteine).